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Trapping hot quasiparticles in a high power superconducting cooler
Hung Q. Nguyen, M. Meschke, J.P. PekolaO.V. Lounasmaa Lab, Aalto University, Finland
C.B. Winkelmann, H. CourtoisInstitut Néel, CNRS, Grenoble, France
Hung Nguyen, Quy Nhon 2013
Basic of cooling using superconducting junctions
Giazotto et.al. RPM, 2006, figure 26Hung Nguyen, Quy Nhon 2013
Two methods to make SINIS coolers
Clark et.al., APL 2004 Lowell et.al., APL 2013
•Photolithography•SINIS with AlMn/Al•Great demonstrations on cooling bulk objects
•E-‐beam lithography•Mostly Cu/Al•Great studies about physics.
Dolan, APL 1977(adapted from Rajauria’s thesis)
Pekola et.al., PRL 2004
Hung Nguyen, Quy Nhon 2013
Our method to make the coolers
Nguyen et.al., APL 2012
Junction size 70x8 µmRN ~1 Ω
Optimum current ~10 µACooling power ~1 nW
•Single vacuum deposition•Trilayer, 2 tunnel barriers•2 steps photolithography•Chemical wet etch Al and Cu•Suspended cooled Cu island
DrainSuperconductor
Trap Cooled island
cooler barrier
drain barrier
resist
AlCu
V
10µm
I
CuAl
AlMn
heat current charge current
Hung Nguyen, Quy Nhon 2013
The role of the drain barrierCooler barrier Drain barrier500 Ωµm2 N/A (no AlMn)500 Ωµm2 1mbar500 Ωµm2 0.2mbar500 Ωµm2 0 mbar
Nguyen et.al., NJP 2013
200 nm
Cooled island200 nm100 nm
V(µV)
IRN
(µA!
)
−300 −200 −100 0 100 200 300−20
−10
0
10
20
T (mK)
T (m
K)
0 100 200 300 4000
100
200
300
400 Ts
Tn
AlAlMn
Cu
Hung Nguyen, Quy Nhon 2013
N1N2 STS1
Dx
S2 z
y
RN
RD
S1 : dSr.(SrTS) = INIS(V, TS , TN , RN )V � PNIS(V, TS , TN , RN )
�PNIS(0, TS , TD, RD)
S2 : dSr.(SrTS) = �PNIS(0, TS , TD, RD)� PNIS(0, TS , TST , RN )
N1 : NdNr2TN = �PNep(TN )
N2 : NdNr2TN = PNIS(V, TS , TN , RN )� PNep(TN )
D : DdDr2TD = PNIS(0, TS , TD, RD)� PDep(TD)
ST : NdNr2TST = PNIS(0, TS , TST , RN )� PSTep (TST ).
A thermal model
Nguyen et.al., NJP 2013Hung Nguyen, Quy Nhon 2013
A thermal modelCooler barrier Drain barrier500 Ωµm2 no AlMn, no TD term500 Ωµm2 500 Ωµm2
500 Ωµm2 10 Ωµm2
Hung Nguyen, Quy Nhon 2013
x (µm)T
(mK)
0 20 40 60 80 100300
350
400
450
500
Ts
TD
V (µV)
T N (m
K)
�� �� �� � ��� ��� ������
���
���
���
TN (mK)
P NIS
(nW
)
0 100 200 3000
0.2
0.4
0.6
0.8
1
Tbath (mK)
T N (m
K)
0 100 200 3000
100
200
300
200 nm
Cooled island200 nm60 nm
Cooler barrier Drain barrier500 Ωµm2 0.2mbar2500 Ωµm2 0.2mbar5000 Ωµm2 0.2mbarAl
AlMn
Coldest T: 30 mK
Cu
The role of the cooler barrier
Q̇ep = ⌃⌦(T 5N � T 5
ph)
Q̇NIS =1
e2RN
ZdE(E � eV )nS(E)[fN (E � eV )� fS(E)]
T phN < Tbath
Hung Nguyen, Quy Nhon 2013
Conclusion
Al AlMn
CuWith good quasiparticle trapping, the SINIS coolers cool from 200 mK to 50 mK at 400 pW per device!
But there are still quasiparticles to trap.
TN (mK)
V opt/!
0 100 200 3000.65
0.7
0.75
0.8
0.85
0.9
0.95
1
V
IRN
−400 −200 0 200 400−20
−10
0
10
20
no qps draingood drain barriergood cooling barrierTheory
(µV)
(µAΩ)
Hung Nguyen, Quy Nhon 2013
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